1. Field of the invention
This application relates to the field of speed responsive engaging devices such as clutches.
2. Prior art
It has been known in the prior art that it is desirable to have a clutch to lock the impeller and turbine elements of a hydrodynamic device together to eliminate slippage therebetween under certain conditions to improve the efficiency of the device. It is further known that it is convenient to use the speed of rotation of an element as a signal to initiate engagement and disengagement of the clutch. The engagement is critical, for example, when the lock-up clutch is used in a hydrodynamic device in combination with an automatic transmission. During an automatic ratio change, it is desirable the clutch be disengaged so that torque changes occurring during the shift will not be harsh, due to the hydrodynamic device absorbing shocks. If the clutch in the hydrodynamic device remains engaged during a shift, the shift control to provide smooth shifts is more exacting since the normal shock absorbing characteristic of the hydrodynamic device is eliminated.
As pointed out, it is known to utilize speed responsive clutches as lock-up clutches in a hydrodynamic device. Normally, to insure that such clutches are engaged at the proper time, expensive and complicated controls of the mechanical, electric or hydraulic type are provided. Controls have been used to insure that the lock-up clutch is not engaged during an automatic shift. In addition, the clutch structures performing such functions are normally in themselves quite complicated.
Accordingly, it is the primary object of the present invention to provide a lock-up clutch for a hydrodynamic device of a simple design which will engage and disengage at the proper time without the use of external control mechanisms to determine the points of engagement and disengagement. Further, it is an object of the present invention to provide a speed and torque responsive clutch in a hydrodynamic device which can be physically accommodated within minimum axial and radial dimensions. Further, it is an important object of the present invention to provide a lock-up clutch for a hydrodynamic device which will automatically permit speed differentials within the device during specific operating conditions such as ratio change.